In some ball valve services, such as in high temperature fluid lines, it is desirable to provide valves with all metalic components, including the seats and seals. When such are employed, it is further desirable to have a sealing force biasing the seat ring against the ball to insure fluid tight sealing. This is conventionally accomplished with use of system pressures, eccentric loading, spring means or a combination thereof. However, if such a force is maintained at all times, it may require excessive torque to operate the valve, and it may result in scoring, wearing and galling of the valve components. Moreover, where corrosive fluids are being handled, spring failures are common and frequent spring replacement and servicing of the valves are necessitated.